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Abstract
The effects of polyunsaturated fatty acids (PUFA) on the structure of recombinant high density lipoprotein (rHDL) was investigated using homogeneous particles containing phosphatidylcholine (PC), [3H]cholesterol, and apolipoprotein A-I (apoA-I). The PC component of the rHDL contained sn -1 16:0 and sn -2 18:1 (POPC), 18:2 (PLPC), 20:4 (PAPC), 20:5 n-3 (PEPC), or 22:6 n-3 (PDPC). The concentration of guanidine HCl (D1/2) required to denature one-half of the apoA-I on rHDL containing long chain PUFA was reduced (1.57-1.70 m) compared to those containing POPC (2.83 m). Intrinsic apoA-I tryptophan fluorescence emission intensity and lifetimes were decreased for rHDL containing long chain PUFA compared to POPC and PLPC rHDL. Monoclonal antibody binding studies demonstrated that apoA-I had decreased immunoreactivity with monoclonal antibodies spanning amino acid residues 115-147 in rHDL containing long chain PUFA. PC lipid fluidity, measured as diphenylhexatriene (DPH) fluorescence polarization, was increased in PUFA rHDL compared to POPC rHDL. There also was a strong correlation between the number of sn -2 double bonds in rHDL and DPH fluorescence lifetime (r 2 = 0. 89). LCAT reactivity of the homogeneous size rHDL was ordered POPC = PLPC>PAPC> PEPC>PDPC. We conclude that rHDL with long chain PUFA in the sn -2 position of PC contain apoA-I that is less stable and in a different conformation than that in POPC rHDL and have a fatty acyl region that is more fluid and hydrated. The weaker interaction of apoA-I with PC containing PUFA may lead to hypercatabolism of apoA-I in plasma explaining, in part, the decreased plasma HDL and apoA-I concentrations seen with PUFA diets.
Highlights
The effects of polyunsaturated fatty acids (PUFA) on the structure of recombinant high density lipoprotein was investigated using homogeneous particles containing phosphatidylcholine (PC), [3H]cholesterol, and apolipoprotein A-I
As recombinant high density lipoprotein (rHDL) heterogeneity has an influence on LCAT reactivity and may influence other physical measurements of rHDL, the objective of this study was to use rHDL that had been purified to apparent size homogeneity
We have previously found that there is a strong association between rHDL apolipoprotein A-I (apoA-I) stability and LCAT activation energy, suggesting that the temperature-dependent step of the LCAT reaction may be sensitive to the strength of the interaction of apoA-I with rHDL PC [16]
Summary
The effects of polyunsaturated fatty acids (PUFA) on the structure of recombinant high density lipoprotein (rHDL) was investigated using homogeneous particles containing phosphatidylcholine (PC), [3H]cholesterol, and apolipoprotein A-I (apoA-I). The type of phospholipid species appears to influence LCAT reactivity through effects at the active site as well as through interfacial effects at the particle surface (i.e., lipid fluidity and apoA-I conformation) [9]. This suggests that changing the phospholipid content of HDL can influence the size of the particles and the functional properties of apoA-I. These studies were carried out with rHDL that were heterogeneous in size and in many cases, contained phospholipid species that are not likely to exist in nascent or plasma HDL
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